Apparatus for encoding and decoding image by skip encoding and method for same

ABSTRACT

The present invention relates to an apparatus and method for encoding and decoding an image by skip encoding. The image-encoding method by skip encoding, which performs intra-prediction, comprises: performing a filtering operation on the signal which is reconstructed prior to an encoding object signal in an encoding object image; using the filtered reconstructed signal to generate a prediction signal for the encoding object signal; setting the generated prediction signal as a reconstruction signal for the encoding object signal; and not encoding the residual signal which can be generated on the basis of the difference between the encoding object signal and the prediction signal, thereby performing skip encoding on the encoding object signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/696,786having a 371(c) date of Nov. 7, 2012, which is a U.S. national stageapplication of International Application No. PCT/KR2011/003401 filed onMay 6, 2011. This application claims the benefit of Korean ApplicationNos. 10-2010-0042823 filed on May 7, 2010; 10-2010-0121192 filed on Dec.1, 2010; and 10-2011-0042990 filed on May 6, 2011. The entire contentsof application Ser. No. 13/696,786, International Application No.PCT/KR2011/003401, and Korean Application Nos. 10-2010-0042823,10-2010-0121192, and 10-2011-0042990 are incorporated herein byreference for all purposes.

BACKGROUND

1. Field

The present invention relates to image signal coding, and moreparticularly, to an apparatus and a method for coding and decoding animage signal using skip coding.

2. Description of Related Art

There is a need to code an image signal so as to effectively write stillpictures or moving pictures in a storage medium or effectively transmitthe still pictures or the moving pictures. Various methods have beenproposed so as to improve efficiency at the time of coding. As arepresentative method, there are a method of using temporal predictionand a method of using spatial prediction.

The temporal prediction is to detect a prediction block having thesmallest residual coefficients for object blocks of a current frame fromother frames temporally approaching the current frame and is referred toas inter prediction.

The spatial prediction uses reconstructed pixel values of referenceblocks adjacent to object blocks within a single frame to obtainprediction pixel values of the object blocks and is referred to as intraprediction.

Deblocking filtering may not be applied to spatially adjacentreconstructed signals that are used during a process of performing theintra prediction according to the related art, such that blockingartifacts occur. In addition, the adjacent reconstructed signals useonly pixels in an integer pel unit. Further, the process of performingthe intra prediction according to the related art is performed by usingonly the object signals of coding and the adjacent reconstructedsignals, such that the spatially limited intra prediction is performed.

SUMMARY

The present invention provides an apparatus and method for coding anddecoding an image using skip coding capable of increasing performance ofcoding and decoding by generating prediction signals similar to codingobject signals using reconstructed signals and skipping residual signalsgenerated by a difference between original image signals and theprediction signals from a coding object during a coding process of animage signal.

The present invention also provides an apparatus and method for codingand decoding an image capable of increasing performance of image signalcoding and decoding by using skip coding during an intra coding process.

In an aspect, there is provided an image coding method using skipcoding, including: performing filtering on signals reconstructed earlierthan coding object signals within coding object images at the time ofperforming intra prediction; generating prediction signals of the codingobject signals using the filtered reconstructed signals; and skip codingthe coding object signals by setting the generated prediction signals asthe reconstructed signals of the coding object signals and by not codingresidual signals generated based on a difference between the codingobject signals and the prediction signals.

The performing of the filtering may perform the filtering by using atleast one of a low pass filter, a deblocking filter, an adaptive loopfilter, an interpolation filter, and a noise removing filter.

The performing of the filtering step-by-step may perform at least one ofa low pass filter, a deblocking filter, an adaptive loop filter, aninterpolation filter, and a noise removing filter.

The performing of the filtering may reconstruct all the reference imagesof the coding object images and then, performs the filtering on thereconstructed reference images, at the time of performing the intraprediction.

The performing of the filtering may partially reconstruct the referenceimages of the coding object images and then, perform the filtering onthe reconstructed reference images, at the time of performing the intraprediction.

The generating of the prediction signals may generate the predictionsignals by performing extrapolation for each direction, based onreconstructed pixels adjacent to the coding object signals.

The generating of the prediction signals may generate the predictionsignals by performing template matching between reconstructed pixelsadjacent to the coding object signals and the filtered reconstructedsignals.

The generating of the prediction signals may generate the predictionsignals by performing displaced intra prediction between the codingobject signals and the filtered reconstructed signals.

The generating of the prediction signals may generate the predictionsignals by performing inter-layer intra prediction, using the filteredreconstructed signals within a base layer spatially corresponding topositions of the coding object signals within an enhancement layer.

The generating of the prediction signals may generate the predictionsignals by performing inter-view intra prediction, using the filteredreconstructed signals within a base view spatially corresponding topositions of the coding object signals within an enhancement view.

The image coding method using skip coding may further includetransmitting an indicator indicating that the coding object signals areskip-coded to a decoder, without coding the residual signals.

In another aspect, there is provided an image coding apparatus usingskip coding, including: a filtering unit that performs filtering onsignals reconstructed earlier than coding object signals within codingobject images at the time of performing intra prediction; a predictionsignal generator that generates prediction signals of the coding objectsignals using the filtered reconstructed signals; a skip coder thatperforms skip coding on the coding object signals by setting thegenerated prediction signals as the reconstructed signals of the codingobject signals and by not coding residual signals generated based on adifference between the coding object signals and the prediction signals;and an indicator indicating that the coding object signals areskip-coded, without coding the residual signals.

In another aspect, there is provided an image decoding method using skipcoding, including: performing filtering on signals reconstructed earlierthan decoding object signals, based on an indicator for skip codingincluded in the decoding object signals within decoding object images,at the time of performing intra prediction; generating predictionsignals of the decoding object signals using the filtered reconstructedsignals; and decoding the decoding object signals by setting thegenerated prediction signals as the reconstructed signals of thedecoding object signals and by not decoding residual signals.

In another aspect, there is provided an image decoding apparatus usingskip coding, including: an indicator for skip coding included indecoding object signals within decoding object images transmitted from askip coder, at the time of performing intra prediction; a filtering unitthat performs filtering on signals reconstructed earlier than thedecoding object signals, based on the indicator; a prediction signalgenerator that generates prediction signals of the decoding objectsignals, based on the filtered reconstructed signals and the indicator;and a skip decoder that decodes the decoding object signals by notdecoding residual signals.

As set forth above, the exemplary embodiment of the present inventioncan provide the apparatus and method for coding and decoding an imageusing the skip coding capable of increasing the performance of codingand decoding by generating the prediction signals similar to the codingobject signals using the reconstructed signals and skipping the residualsignals generated by the difference between the original image signalsand the prediction signals from the coding object during the codingprocess of the image signal.

In addition, the exemplary embodiment of the present invention canremove image noise, blocking artifacts, quantization errors, aliasing,or the like, by performing various filtering on the reconstructeddecoding object images or the previously reconstructed images.

Further, the exemplary embodiment of the present invention can generatethe prediction signals similar to the coding object signals by using thefiltered reconstructed signals through various methods.

Moreover, the exemplary embodiment of the present invention can increasethe performance of the image coding by skipping the coding process ofthe residual signals that are generated by the difference between theoriginal image signals and the prediction signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an image coding apparatus using skip codingaccording to an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing an example of an image coding process usingskip coding according to the exemplary embodiment of the presentinvention.

FIG. 3 is a block diagram of an image decoding apparatus using skipcoding according to another exemplary embodiment of the presentinvention.

FIG. 4 is a flow chart of an image coding method using skip codingaccording to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 shows a block diagram of an image coding apparatus using skipcoding according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the image coding apparatus using skip codingaccording to the exemplary embodiment of the present invention mayinclude a filtering unit 110, a prediction signal generator 120, a skipcoder 130, and an indicator 140.

The filtering unit 110 performs filtering on reconstructed signalsearlier than coding object signals within coding object images at thetime of performing intra prediction. The coding object image means aportion to be coded in original images. The coding object image may beall of the original images and a portion of the original images. Thecoding object image may include the coding object signal. The codingobject signals may be signals obtained by differentiating the codingobject image in a unit of a pixel, a block, a unit, a picture, and aframe. That is, the coding object signals conceptually include a codingobject pixel, a coding object block, a coding object unit, a codingobject picture, and a coding object frame. The coding object images mayinclude signals reconstructed earlier than the coding object signals.The reconstructed signals may include signals reconstructed after someof the plurality of signals included in the coding object image aresubjected to coding.

The filtering unit 110 performs low pass filtering on the signalreconstructed earlier than the coding object signals, thereby reducingnoise present in the reconstructed signals. In this case, the filtercoefficients used for the low pass filter are coded, which may be inturn transmitted to a decoder.

For example, low pass filtering may be performed on adjacentreconstructed reference samples used at the time of performing the intraprediction. In this case, the filtering may be performed one time, twotimes, N_(f) times, or the like. In this case, N_(f) indicates anypositive integer.

In addition, whether the filtering is performed may depend on codingparameters. That is, it may be determined whether the filtering isapplied according to the block size of the coding object signals, theintra prediction mode, whether there are residual signals in theadjacent blocks, whether constrained intra prediction (CIP) is used, andat least one discrimination among the intra prediction directionsimilarities of the adjacent blocks.

In addition, if it is determined that the filter is applied, a tap sizeindicating the number of input samples of the filter, coefficients ofthe low pass filter, filter strength, or the like, may differ. In thiscase, the tap size may perform the filtering by using at least onefilter tap among 2-tap, 3-tap, and Nt-tap. In this case, N_(t) indicatesany positive integer.

In addition, the filtering unit 110 may perform deblocking filter on thereconstructed signals to reduce the blocking artifacts present in thereconstructed signals. The blocking artifacts occur due to errors ofquantization that is performed during the image coding process.

For example, the deblocking filter may be performed as follows.

First, it is possible to discriminate a boundary of the objects to befiltered. Basically, it may be determined that the images used duringthe image coding and decoding processes is the boundary of the objectsto be filtered in a coding and decoding unit where the image ispartitioned.

In this case, any one of a boundary of coding units, a boundary ofprediction units, and a boundary of transform units may be the boundaryof the objects to be filtered. The filtering of boundary discriminationmay be performed as a unit of a coding unit, a unit of the largestcoding unit (LCU), a slice unit, and a picture unit.

Second, it may be determined whether the filtering is performed by usingat least one of result values of a formula using the filter strength ofthe boundary of the filtering objects and pixel values around theboundary.

For example, the filter strength may indicate the tap size indicatingthe number of input samples of the low pass filter, the coefficients ofthe low pass filter, or the like, when the filtering is performed on thereconstructed samples present around the boundary. In this case, thecoding parameters may be used so as to determine the filter strength.For example, at least one of an intra prediction mode, an interprediction mode, a motion vector, a reference image index, and a codingblock flag may be used. For example, the result values of the formulausing the pixel values around the boundary may discriminate whether thefiltering object boundary is the blocking artifacts due to the transformand the quantization or real edges present in the image.

Third, the filtering is performed on the filtering object boundary byusing the information regarding the determined filtering object boundaryand whether the filtering is performed. In this case, the filtering maybe performed by the low pass filter that smoothes the pixel valuesaround the boundary so that the edge due to variation of pixel value,etc., is not visible to the human eye and a Wiener filter so as tominimize distortion in the original images, or the like, on the basis ofvariations of the pixel values around the boundary, or the like. Inaddition, a one-dimensional filter or a multi-dimensional filter of twodimensions or more may be used according to the filtering objectboundary.

For example, the multi-dimensional filter of two dimensions or more mayhave a shape of the filter, such as quadrangle, circle, rectangle, orthe like, and a structure of the filter coefficients, such as ahorizontal symmetry, a vertical symmetry, a diagonal symmetry, or thelike.

In addition, the above-listed various filters may be used in a filteringexecution unit according to the filter strength determined in a unit ofdetermining whether the filtering is performed, or the like. Forexample, when the coding and decoding processes including the intraprediction, the inter prediction, the transform/inverse transform, thequantization/dequantization, and the entropy coding/entropy decoding areperformed in the slice unit, the unit of the largest coding unit (LCU),or the unit of the coding unit (CU), while the deblocking filtering maybe performed in the slice unit, the unit of the LCU, or the unit of theCU. When the series of coding and decoding processes including thedeblocking filtering are performed in the coding and decoding object LCUand the spatially adjacent LCU, the reconstructed samples in the LCUthat are subjected to the deblocking filtering may be used at the timeof performing the intra prediction of the coding and decoding objectLCU. That is, the reconstructed samples in the LCU that are subjected tothe deblocking filtering may be used in the following prediction signalgenerator 120.

In addition, the filtering unit 110 performs an adaptive loop filteringon the reconstructed signals based on the Wiener filter, therebyreducing the quantization errors present in the reconstructed signals.In this case, the filter coefficients used for the adaptive loop filterare coded, which may be in turn transmitted to the decoder.

For example, the adaptive loop filtering may be performed as follows.

The filtering may be performed on the reconstructed samples, to whichthe deblocking filtering is applied, in the sample unit or an N×M (N andM are any positive integer) block unit, based on the adaptive loopfilter coefficients transmitted to the decoder. In this case, thesamples and the blocks to which the adaptive loop filtering is appliedmay be determined using a filter map indicating whether the adaptiveloop filtering is performed. The filter map may be transmitted from thecoder to the decoder, being included in a bitstream, together with thefilter coefficients. In addition, the filter may differ according to thesamples and the blocks to which the adaptive loop filter is applied andvarious filter tap sizes and filter shapes may be used. When theadaptive loop filtering is applied to the samples and the blocks, whatfilter is used may be determined by the formula using the reconstructedsamples to which the deblocking filtering is applied.

For example, when the coding and decoding processes including the intraprediction, the inter prediction, the transform/inverse transform, thequantization/dequantization, the entropy coding/entropy decoding, andthe deblocking filtering are performed in the adaptive loop filtering inthe slice unit, the unit of the largest coding unit (LCU), or the unitof the coding unit (CU), while the adaptive loop filtering may beperformed in the slice unit, the unit of the LCU, or the unit of the CU.In this case, when the series of coding and decoding processes includingthe adaptive loop filtering are performed in the coding and decodingobject LCU and the spatially adjacent LCU, the reconstructed samples inthe LCU that are subjected to the adaptive loop filtering may be used atthe time of performing the intra prediction of the coding and decodingobject LCU. That is, the reconstructed samples in the LCU that aresubjected to the adaptive loop filtering may be used in the followingprediction signal generator 120.

In addition, the filtering unit 110 performs interpolation filtering onthe reconstructed signals, thereby reducing an aliasing phenomenonpresent in the reconstructed signals. The filtering unit 110 may performthe interpolation filtering in a sub-pel unit. In this case, theinterpolation filtering of the reconstructed signals may be performed ona luminance signal of ½ precision, a chrominance signal of ¼ precision,or the like. An example of the interpolation filtering method mayinclude a bilinear interpolation method, an average interpolatingmethod, or the like and the interpolation filtering may be performedwith ⅛, 1/16, 1/32, 1/N_(i) (_(Ni) is any integer), or the like. In thiscase, the interpolated samples may be used in the prediction signalgenerator 120. That is, the interpolated values may be the predictionsignals and new prediction signals may be generated by using theinterpolated values.

In addition, the filtering unit 110 may perform noise removing filteringfrom the reconstructed signals to remove or reduce the noise present inthe reconstructed signals.

In addition, the filtering performed in the filtering unit 110 may beapplied to both of the luminance components and the chrominancecomponents of the reconstructed signals.

In addition, the filtering unit 110 may perform the filtering on thereconstructed reference images after all the reference images of thecoding object images are reconstructed at the time of performing theintra prediction or the inter prediction and may perform the filteringon the reconstructed reference images after the reference images of thecoding object images are partially reconstructed. In this case, thefiltering unit 110 may step-by-step perform at least one of the low passfilter, the deblocking filter, the adaptive loop filter, theinterpolation filter, and the noise removing filter on the reconstructedsignals.

For example, the low pass filter may be performed on the reconstructedsignals and the deblocking filter may be performed on the reconstructedsignals on which the low pass filter is performed.

For example, the low pass filter may be performed on the reconstructedsignals and the interpolation filter may be performed on thereconstructed signals on which the low pass filter is performed.

For example, the deblocking filter may be performed on the reconstructedsignals and the adaptive loop filter may be performed on thereconstructed signals on which the deblocking filter is performed.

For example, the adaptive loop filter may be performed on thereconstructed signals and the interpolation filter may be performed onthe reconstructed signals on which the adaptive loop filter isperformed.

For example, the low pass filter may be performed on the reconstructedsignals, the deblocking filter may be performed on the reconstructedsignals on which the low pass filter is performed, and the adaptive loopfilter may be performed on the reconstructed signals on which the lowpass filter and the deblocking filter is performed.

For example, the low pass filter may be performed on the reconstructedsignals, the deblocking filter may be performed on the reconstructedsignals on which the low pass filter is performed, and the interpolationfilter may be performed on the reconstructed signals on which the lowpass filter and the deblocking filter is performed.

For example, the deblocking filter may be performed on the reconstructedsignals, the adaptive loop filter may be performed on the reconstructedsignals on which the deblocking filter is performed, and theinterpolation filter may be performed on the reconstructed signals onwhich the deblocking filter and the adaptive loop filter are performed.

As in the above example, the reconstructed signals on which variousfilters are performed step-by-step may be used in the followingprediction signal generator 120.

The prediction signal generator 120 may generate the prediction signalsof the coding object signals by using the reconstructed signals filteredby the filtering unit 110.

The prediction signal generator 120 may generate the prediction signalsby performing template matching. The template matching may be performedusing pixel similarity between the reconstructed pixels adjacent to thecoding object signals and the reconstructed signals filtered by thefiltering unit 110. In this case, the pixel similarity may be measuredby sum of absolute difference (SAD), sum of absolute transformeddifference (SATD), and sum of squared difference (SSD).

When template matching is performed, since the reconstructed pixelsadjacent to the coding object signals from the coder and the decodingobject signals from the decoder are the same, the same predictionsignals may be generated in the coder and the decoder without a separateindicator for template matching. That is, the coder and the decoder maygenerate the prediction signals by using the same template. The size ofthe template used for template matching may be adaptively selectedaccording to an operation processing rate in the image coding process, amemory, or the like. Further, the prediction signal generator 120 maygenerate the prediction signals by using the plurality of filteredreconstructed signals among the filtered reconstructed signals.

In addition, the prediction signal generator 120 may generate theprediction signals by performing displaced intra prediction. Thedisplaced intra prediction may be performed using the pixel similaritybetween the coding object signals and the reconstructed signals filteredby the filtering unit 110.

The displaced intra prediction uses displacement vectors. Thedisplacement vectors indicate positions of the filtered reconstructedsignals having the most similar values to the coding object signals. Thecoder may transmit the displacement vectors to the decoder and thedecoder may generate the same prediction signals as the coder using thereconstructed signals present in the positions of the displacementvectors. The decoder may generate the prediction signals without greatlyincreasing computation complexity by using the displacement vectorstransmitted from the coder. In addition, the prediction signal generator120 may use, as the displacement vector prediction values of the codingobject signals, the displacement vectors present in the reconstructedsignals around the coding object signals. The prediction signalgenerator 120 may generate the prediction signals by searching theadjacent areas of the coding object signals based on the displacementvector prediction values. In addition, the coder may transmit thedisplacement vector prediction values and difference values between thedisplacement vectors of the adjacent areas searched in the coding objectsignals to the decoder.

In addition, the prediction signal generator 120 may search the mostsimilar initial point to the coding object signals among the filteredreconstructed signals by performing template matching and may generatethe prediction signals by performing the displaced intra prediction atthe initial point. In addition, the prediction signal generator 120 maysearch the most similar initial point to the coding object signals amongthe filtered reconstructed signals by performing the displaced intraprediction and may generate the prediction signals by performingtemplate matching at the initial point.

Further, the prediction signal generator 120 performs the reconstructedpixels adjacent to the coding object signals to perform line based intraprediction, thereby generating the prediction signals. The line basedintra prediction is a method of performing extrapolation on thereconstructed pixels around the coding object signals, for eachdirection based on the coding object signals.

In this case, the number of directions may be at least one, that is,plural. For example, the number of directions may be 2, 4, 8, 16, 33, orthe like. The directions and the number of directions may be fixed inadvance. Further, the directions and the number of directions may beadaptively defined using the reconstructed pixels.

In this case, when extrapolation is performed for each direction, thefiltering unit 110 may use at least one method. For example,extrapolation may be performed using the signals obtained according towhether the low pass filter is applied and by making the methoddifferent or according to whether the interpolation filter is appliedand by making the method different, for each direction.

In addition, a weighted sum of at least two reconstructed pixels may beused at the time of performing the extrapolation and weights may differaccording to a size of a distance or a block. For example, the weightedsum of the prediction signals corresponding to the similar directionsmay be final prediction signals.

In addition, the prediction signal generator 120 uses the reconstructedsignals in a base layer spatially corresponding to the positions of thecoding object signals and the coding object signals within anenhancement layer having spatial resolution, image quality, frame rate,or the like, that are equal to or higher than a base layer to performinter-layer intra prediction, thereby generating the prediction signals.

For example, when the spatial resolution of the base layer is equal tothe spatial resolution of the enhancement layer, the reconstructedsignals within the base layer are used in the intra prediction of thecoding object signals within the enhancement layer, thereby generatingthe prediction signals.

For example, when the spatial resolution of the base layer is differentfrom the spatial resolution of the enhancement layer, the reconstructedsignals within the base layer are used in the intra prediction of thecoding object signals within the enhancement layer by controlling thespatial resolution of the base layer through upsampling or downsampling,or the like, so as to match the spatial resolution of the enhancementlayer, thereby generating the prediction signals.

In addition, the prediction signal generator 120 uses the coding objectsignals within an enhancement view and the reconstructed signals withina base view spatially corresponding to the positions of the codingobject signals to perform inter-view intra prediction, therebygenerating the prediction signals.

For example, when the spatial resolution of the base view is equal tothe spatial resolution of the enhancement view, the reconstructedsignals within the base view are used in the intra prediction of thecoding object signals within the enhancement view, thereby generatingthe prediction signals.

For example, when the spatial resolution of the base view is differentfrom the spatial resolution of the enhancement view, the reconstructedsignals within the base view are used in the intra prediction of thecoding object signals within the enhancement view by controlling thespatial resolution of the base view through the upsampling or thedownsampling, or the like, so as to match the spatial resolution of theenhancement view, thereby generating the prediction signals.

In addition, the prediction signal generator 120 may generate theprediction signals by using the coding object signals partitioned intothe blocks having any size. In this case, the prediction signals may begenerated by one of the line based intra prediction, template matching,the displaced intra prediction, the inter-layer intra prediction, andthe inter-view intra prediction. The prediction signal generator 120 maygenerate the prediction signals using the plurality of partitionedcoding object signals by the method of generating the same predictionsignals and/or by the method of generating different prediction signals.

The skip coder 130 sets the prediction signals generated in theprediction signal generator 120 as the reconstructed signals of thecoding object signals. The set reconstructed signals may be used at thetime of coding the next coding object signals of the coding objectimages. In addition, the skip coder 130 performs the skip coding on thecoding object signals by not coding the residual signals. The skip coder130 does not perform the transform coding, the quantization, and theentropy coding on the residual signals.

The skip coder 130 may perform the skip coding by partitioning thecoding object signals into any block size. In this case, the block sizeof the coding object signals that are skip-coded may be determined as asize of any integer N×M. The information regarding the indicator and theblock size for the skip coding corresponding to the block size of eachcoding object signal may be transmitted to the decoder as many as anyinteger L per a macroblock. When the macroblock is partitioned into asize of N×M, the number of blocks included in the macroblock may bereferred to L.

The indicator 140 may indicate that the coding object signals areskip-coded without coding the residual signals. The indicator 140indicating the skip coding may have a flag type or a macroblock modetype. In addition, the indicator 140 may indicate the method ofgenerating the prediction signals. That is, the indicator 140 mayindicate that the prediction signals are generated by any one of theline based intra prediction, the template matching, the displaced intraprediction, the inter-layer intra prediction, and the inter-view intraprediction. In this case, the indicator 140 indicating the method ofgenerating the prediction signals may have a flag type or a macroblockmode type. In addition, the indicator 140 may indicate a filteringmethod. The indicator 140 may indicate that the filtering is performedby any one of the filtering methods for the reconstructed signalsincluding the low pass filter, the deblocking filter, the adaptive loopfilter, the interpolation filter, or the noise removing filter. Inaddition, the indicator 140 may indicate that at least one of thefiltering methods for the reconstructed signals is performed. Forexample, the indicator 140 may indicate whether the low pass filter isapplied to the reconstructed signals and the deblocking filter isapplied thereto, whether the low pass filter is applied to thereconstructed signals and the interpolation filter is applied thereto,whether the deblocking filter is applied to the reconstructed signalsand the adaptive loop filter is applied thereto, whether the adaptiveloop filter is applied to the reconstructed signals and theinterpolation filter is applied thereto, whether the low pass filter isapplied to the reconstructed signals, whether the deblocking filter isapplied thereto and the adaptive loop filter is applied thereto, whetherthe low pass filter is applied to the reconstructed signals, thedeblocking filter is applied thereto, and the interpolation filter isapplied thereto, and the deblocking filter is applied to thereconstructed signals, the adaptive loop filter is applied thereto, andthe interpolation filter is applied thereto. In this case, the indicator140 for the filtering method may have a flag type or a macroblock modetype.

The coder performs entropy coding on the indicator by arithmetic coding,variable length coding, or the like, and inserts the coded indicatorinto a bitstream. The decoder performs entropy decoding on the entropycoded indicator in the bitstream, thereby discriminating whether theskip coding is performed, the method of generating the predictionsignals, or the filtering method.

The indicator 140 indicating the skip coding, the method of generatingthe prediction signals, and the filtering method may be transmitted fromthe coder to the decoder. In this case, the decoder may use theprediction signals generated in the decoder as the reconstructed signalsof the decoding object signals without decoding the residual signals.

FIG. 2 is a diagram showing an example of the image coding process usingthe skip coding according to the exemplary embodiment of the presentinvention.

Referring to FIG. 2, an image coding apparatus using the skip codingaccording to the exemplary embodiment of the present invention performsthe skip coding on original images 210 in a block unit. That is, thecoding object signals may also be the coding object blocks. The codingobject image 220 may include a coding object A block 221 and a B block223 reconstructed earlier than the coding object A block 221. Thefiltering unit 110 performs filtering on the reconstructed B block 223.In this case, the filtering may be performed using at least one of thelow pass filter, the deblocking filter, the adaptive loop filter, theinterpolation filter, or the noise removing filter on the reconstructedsignals. The filtering unit 110 may generate a C block 230 by performingthe filtering on the reconstructed B block 223. The predictive signalgenerator 120 generates a predictive D block 240 of the coding object Ablock 221 by using the C block 230. In this case, the predictive D block240 may be generated by one of the line based intra prediction, thetemplate matching, the displaced intra prediction, the inter-layer intraprediction, or the inter-view intra prediction. The skip coder 130 maybe set the predictive D block 240 as the reconstructed blocks of thecoding object A block 221. The reconstructed block may be used when theB block is skip-coded. The skip coder 130 may generate a remaining Eblock 250 by removing the predictive D block 240 from the coding objectA block 221. The skip coder 130 may perform the skip coding on thecoding object A block 221 by not coding the remaining E block 250included in the coding object A block 221. The skip coder 130 maygenerate a block 260 that is skip-coded. Thereafter, the coding objectimage 220 may be skip-coded by continuously setting a B block 270 as thecoding object block.

FIG. 3 is a block diagram of an image decoding apparatus using skipcoding according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the image decoding apparatus using the skip codingaccording to the exemplary embodiment of the present invention mayinclude an indicator 310, a filtering unit 320, a prediction signalgenerator 330, and a skip decoder 340.

The indicator 310 may indicate that the skip coder performs the skipcoding on the coding object signals without coding the residual signalsat the time of performing the intra prediction. The indicator 310indicating the skip coding may have a flag type or a macroblock modetype. The indicator 310 may be identified while being included in thedecoding object signal within the decoding object images. In addition,the indicator 310 may indicate the method of generating the predictionsignals during the skip coding process. That is, the indicator 310 mayindicate that the prediction signals of the coding object signals aregenerated by any one of the line based intra prediction, templatematching, the displaced intra prediction, the inter-layer intraprediction, and the inter-view intra prediction. In addition, theindicator 310 may indicate the filtering method. That is, the indicator310 may indicate that the filtering is performed by any one of thefiltering methods for the reconstructed signals including the low passfilter, the deblocking filter, the adaptive loop filter, theinterpolation filter, or the noise removing filter. In addition, theindicator 310 may indicate that at least one of the filtering methodsfor the reconstructed signals is performed. For example, the indicator310 may indicate whether the low pass filter is applied to thereconstructed signals and the deblocking filter is applied thereto,whether the low pass filter is applied to the reconstructed signals andthe interpolation filter is applied thereto, the deblocking filter isapplied to the reconstructed signals and the adaptive loop filter isapplied thereto, whether the adaptive loop filter is applied to thereconstructed signals and the interpolation filter is applied thereto,whether the low pass filter is applied to the reconstructed signals, thedeblocking filter is applied thereto, and the adaptive loop filter isapplied thereto, whether the low pass filter is applied to thereconstructed signals, the deblocking filter is applied thereto, and theinterpolation filter is applied thereto, and the deblocking filter isapplied to the reconstructed signals, the adaptive loop filter isapplied thereto, and the interpolation filter is applied thereto. Thecoder performs the entropy coding on the indicator by the arithmeticcoding, the variable length coding, or the like, and inserts the entropycoded indicator into the bitstream. The decoder performs the entropydecoding on the entropy coded indicator 310 in the bitstream, therebydiscriminating whether or not the skip coding is performed, the methodof generating the prediction signals, or the filtering method.

The filtering unit 320 performs the filtering on the signalsreconstructed earlier than the decoding object signals, based on thefiltering method used during the process of coding the indicator 310.The decoding object signals may be signals obtained by differentiatingthe decoding object images in a unit of a pixel, a block, a unit, apicture, and a frame. That is, the decoding object signals conceptuallyinclude a decoding object pixel, a decoding object block, a decodingobject unit, a decoding object picture, and a decoding object frame. Thefiltering unit 320 similar to the filtering unit 110 of the image codingapparatus using the skip coding may perform the filtering using at leastone of the low pass filter, the deblocking filter, the adaptive loopfilter, the interpolation filter, or the noise removing filter on thereconstructed signals. In this case, the filtering unit 320 maystep-by-step perform at least one of the low pass filter, the deblockingfilter, the adaptive loop filter, the interpolation filter, or the noiseremoving filter on the reconstructed signals. The filtering unit 320 mayperform filtering on the reconstructed signals by similarly applying thefiltering method that is applied during the coding process.

The prediction signal generator 330 generates the prediction signals ofthe decoding object signals, based on the reconstructed signals filteredin the filtering unit 320 and the indicator 310. The prediction signalgenerator 330 may generate the prediction signals of the decoding objectsignals, based on the method of generating the prediction signals usedduring the process of coding the indicator 310. The prediction signalgenerator 330 may generate the prediction signals of the decoding objectsignals by one of the line based intra prediction, the templatematching, the displaced intra prediction, the inter-layer intraprediction, and the inter-view intra prediction. The prediction signalgenerator 330 may generate the prediction signals of the decoding objectsignals by applying a method similar to the method of generating theprediction signals applied by the prediction signal generator 120 duringthe coding process.

The skip decoder 340 decodes the decoding object signals using theprediction signals without decoding the residual signals. The skipdecoder 340 performs the skip decoding on the decoding object signals bynot decoding the residual signals in the decoding object signals. Theskip decoder 340 does not perform the inverse transform, thedequantization, and the entropy decoding on the residual signals.

FIG. 4 is a flow chart of the image coding method using the skip codingaccording to another exemplary embodiment of the present invention.

At step 410, the image coding apparatus using the skip coding accordingto the exemplary embodiment of the present invention performs filteringon the signals reconstructed earlier than the coding object signalswithin the coding object images at the time of performing the intraprediction. In this case, the filtering may be performed using at leastone of the low pass filter, the deblocking filter, the adaptive loopfilter, the interpolation filter, and the noise removing filter on thereconstructed signals. In this case, the filtering may be step-by-stepperformed using at least one of the low pass filter, the deblockingfilter, the adaptive loop filter, the interpolation filter, or the noiseremoving filter on the reconstructed signals.

At step 420, the image coding apparatus using the skip coding accordingto the exemplary embodiment of the present invention generates theprediction signals of the coding object signals by using the filteredreconstructed signals. In this case, the prediction signals may begenerated by one of the line based intra prediction, template matching,the displaced intra prediction, the inter-layer intra prediction, andthe inter-view intra prediction.

At step 430, the image coding apparatus using the skip coding accordingto the exemplary embodiment of the present invention sets the generatedprediction signals as the reconstructed signals of the coding objectsignals. The set reconstructed signals may be used at the time of codingthe next coding object signals of the coding object images.

At step 440, the image coding apparatus using the skip coding accordingto the exemplary embodiment of the present invention performs the skipcoding on the coding object signals by not coding the residual signals.

As described above, the coded image data are transmitted to the imagedecoding apparatus as shown in FIG. 3. The image decoding apparatus mayperform the image decoding method as described above in detail in thedescription of FIG. 3, according to the above-mentioned image codingmethod (see FIG. 4).

The methods according to the exemplary embodiment of the presentinvention may be implemented as a program instruction type that may beperformed through various computer units and may be recorded in acomputer readable medium. The computer readable medium may includeprogram instructions, data files, data structure, or the like, alone ora combination thereof. The program instructions recorded in the mediummay be ones particularly designed and configured to meet the presentinvention, computer software, or usable ones known to those skilled inthe art.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

Accordingly, such modifications, additions and substitutions should alsobe understood to fall within the scope of the present invention.

What is claimed is:
 1. An image decoding method performed by a decodingapparatus, comprising: determining whether to perform filtering onsignals to be used in generating intra prediction signals of decodingobject signals, the signals being reconstructed earlier than thedecoding object signals, the signals being adjacent to the decodingobject signals; performing the filtering on the signals in response tothe determination that the filtering is performed; and generating theintra prediction signals of the decoding object signals using thefiltered signals; wherein the determination of whether to perform thefiltering is based on a block size of the decoding object signals and anintra prediction mode of the decoding object signals, and wherein a tapsize of a filter used in the filtering is variable.
 2. The imagedecoding method of claim 1, wherein a strength of the filter used in thefiltering is variable.
 3. The image decoding method of claim 2, whereinthe strength of the filter is determined based on a flag transmittedfrom an encoding apparatus, the flag indicating the strength of thefilter.